1. Field of the Invention
The present invention relates to a surface mounting type planar magnetic device and production method thereof.
2. Description of the Related Art
In recent years, use of portable apparatuses driven by battery such as mobile phone and notebook-type personal computer has been accelerated. Since before, reduction of the weight and size of such portable apparatuses has been demanded and in addition to this demand, recently, higher functions such as communication function, display function and high-speed processing function for a large amount of information including image data have been also requested. Correspondingly, a demand for a power supply capable of transforming a single voltage from a battery to voltage levels necessary for various mounted devices such as CPU, LCD module, and communication power amplifier has been increased. Thus, to achieve the higher function as well as reduction of the size and weight, it has been an important theme to accelerate reductions of the size and thickness of such a magnetic device as transformer and inductor and the like to be mounted on the power supply.
Under this condition, a transformer or an inductor composed of sintered ferrite wound with coil is loaded on the conventional small portable apparatus. However, these components are difficult to thin thereby obstructing thinning of a power supply unit. A planar inductor composed of metal magnetic film layer, insulating layer, planar coil layer, insulating layer and metallic magnetic film layer on Si substrate in order to reduce the size and weight thereof has been described in Journal of the Magnetic Society of Japan 20(1996), pp. 922-924 and disclosed in Japanese Patent Application Laid-Open No. 4-363006. However, these conventional planar inductors have problems in terms of production cost and characteristic. That is, because metal magnetic film of 6 to 7 μm is formed by spattering method and an insulating layer needs to be formed between the metal magnetic film and the planar coil, production cost for the planar inductor is sure to rise with respect to the conventional magnetic device.
The problems in terms of the characteristic are as follows. Because the planar inductor is driven by high frequency in MHz band, power loss is increased by generation of eddy current inside metal magnetic film which is electrically conductive. As for another characteristic problem, because upper and lower metal magnetic layers oppose each other through a slight nonmagnetic space, vertical alternate magnetic flux intersects the planar coil, so that eddy current is generated thereby increasing power loss. For the former, it has been proposed to divide the eddy current to small parts by forming a high resistance region on the same plane as the metal magnetic film according to Japanese Patent Application Laid-Open No. 6-77055 and for the latter, it has been proposed to divide the planar coil conductor to small parts according to Japanese Patent Application Laid-Open No. 9-134820 in order to improve the characteristics. However, it cannot be said that the characteristics have been improved sufficiently.
To solve these problems, Japanese Patent Application Laid-Open No. 11-26239 has disclosed a planar magnetic device employing a ferrite magnetic film formed by printing method or sheet method instead of the metal magnetic film. According to this method, magnetic paste produced by mixing binder with ferrite powder is printed on Si substrate and baked so as to produce a high resistance ferrite magnetic film. After a coil pattern is formed on this film by the plating method, ferrite magnetic film is formed thereon so as to produce a magnetic device. However, this publication has not disclosed an external electrode which is a feature of the present invention, and further surface mount technology (SMT) cannot be applied.